Split_DNS: inbound NAT rule(on Firewall) required ?

Hi,

we are going to test install ZCS in a non direct mail delivery environment.
(downloading mails with fetchmail/POP3 stored at different email-accounts
at different ISPs to our main "Zimbra" account/box (e.g. info@mycompany.com) .
For that test env we will get a(1) Dyn Ip from DynDNS.org.

Questions:
Is for such a scenario an "inbound NAT rule" (on the firewall) required?

If you are going to use fetchmail then a inbound NAT would not be required. You will however need to ensure that a internal MX and A record are available in DNS, so as in your title you will require a Wiki :: Split DNS architecture.